In order to lower the cost of communications, it has become desirable to increase the data rate and the number of communication channels available. This is particularly true in fiber optic communication systems.
In fiber optic communication systems, wavelength division multiplexing (WDM) has been used over the same fiber optic communication link so that multiple channels of communication may be established over one fiber optic cable. The multiple channels of communication are established at different center wavelengths of light. However, the complexity of WDM and its higher data rates makes it expensive to use in low cost applications.
In the data link between fiber-optic transceivers, an emphasis has been placed on improving the electrical-to-optical (EO) and optical-to-electrical (OE) elements in order to provide for the increased data rates over the fiber optic cables. For example, the laser driver driving a semiconductor laser has been improved in order to maintain a wide data eye from transmitter to receiver and avoid data bit errors at high data rates. While these improvements have marginally increased the data rate, they have not alleviated the need for high capacity optical links with lower cost and simpler operation.
Additionally, the medium of the fiber optic cable used has been compensated for various optical signal impairments in order to accommodate higher data rates and reduce some types of distortion. However, current compensation techniques operating in the optical domain are bulky, expensive, and consume too much power. Moreover, these techniques only compensate for one type of distortion at a time, such as chromatic dispersion, and ignore other types of distortions. Furthermore, adding optical signal distortion compensators along an optical cable renders the network provisioning process more complicated and significantly increases the network operational expenses. Additionally, replacing existing lower data rate engineered fiber optic cables with compensated cables to lower distortion and to support higher data rates is very expensive.
In the electrical domain, however, continuous time filters (CTFs) are important features for distortion reduction, especially when used as part of electrical dispersion compensation (EDC) circuitry in fiber optic transceivers. However, current CTFs tend to utilize passive components, such as inductors and resistors, in their design. These passive components suffer from significant impedance variations, especially in response to process variations. These impedance variations may adversely affect the the yield of EDC ASICs and reliability of the fiber optic transceivers. Also, these passive components are unsuitable for on-chip implementations that have significant size constraints.
The need for improved, cost-efficient distortion-mitigating techniques is important to lower the cost of today's optical communications networks, enhance their performance, streamline and simplify their deployment and operation. This need has lead to an improved continuous time filtering as described below.